The present invention relates in general to the manufacture of ring members of a preferred geometry and, in particular, to a method and apparatus for forming a drum or barrel handling ring having an inverted frustoconical shape to facilitate engagement of the top flange or "toe" of the ring with a conventional parrot beak gripper.
It is well known in the art of bending that a straight strip of plastic or the like, having an asymmetrical cross section, has a tendency to twist or shift out of the plane in which it is being bent due primarily to its cross section asymmetry. Upon bending, some portions of the strip are placed in tension, while other portions of the strip are placed in compression. Where the strip being bent has a symmetrical cross section, relative to the bending plane, the tension and compression forces tend to balance each other to allow undistorted planar bending of the strip. On the other hand, such tension and compression forces are unbalanced in the case of bending a strip of material having an asymmetrical cross section. Such force imbalance can result in twisting, distortion, etc. as the strip is bent, for example, into a ring member.
It is recognized that a straight, generally flat strip of thermoplastic material (having a conventional asymmetrical cross section suitable for purposes of forming a drum handling ring), when bent into a ring shape, will form a frustoconically shaped ring with its top flange or "toe" located radially inwardly of the base portion of the ring that engages and mates with a circumferential groove in the drum on which the ring is mounted. Such an "inboard toe" makes it more difficult for a conventional parrot beak gripper to engage the "toe" of the ring.
It would be desirable to form from straight strip stock a drum handling ring having an "outboard toe", i.e. a top flange or "toe" that extends radially outwardly from the base portion of the drum handling ring engaging the associated drum, whereby a conventional parrot beak gripper can easily engage the "outboard toe" of the handling ring.